garbage_test.go

Documentation: runtime/debug

     1  // Copyright 2013 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package debug_test
     6  
     7  import (
     8  	"internal/testenv"
     9  	"os"
    10  	"runtime"
    11  	. "runtime/debug"
    12  	"testing"
    13  	"time"
    14  )
    15  
    16  func TestReadGCStats(t *testing.T) {
    17  	defer SetGCPercent(SetGCPercent(-1))
    18  
    19  	var stats GCStats
    20  	var mstats runtime.MemStats
    21  	var min, max time.Duration
    22  
    23  	// First ReadGCStats will allocate, second should not,
    24  	// especially if we follow up with an explicit garbage collection.
    25  	stats.PauseQuantiles = make([]time.Duration, 10)
    26  	ReadGCStats(&stats)
    27  	runtime.GC()
    28  
    29  	// Assume these will return same data: no GC during ReadGCStats.
    30  	ReadGCStats(&stats)
    31  	runtime.ReadMemStats(&mstats)
    32  
    33  	if stats.NumGC != int64(mstats.NumGC) {
    34  		t.Errorf("stats.NumGC = %d, but mstats.NumGC = %d", stats.NumGC, mstats.NumGC)
    35  	}
    36  	if stats.PauseTotal != time.Duration(mstats.PauseTotalNs) {
    37  		t.Errorf("stats.PauseTotal = %d, but mstats.PauseTotalNs = %d", stats.PauseTotal, mstats.PauseTotalNs)
    38  	}
    39  	if stats.LastGC.UnixNano() != int64(mstats.LastGC) {
    40  		t.Errorf("stats.LastGC.UnixNano = %d, but mstats.LastGC = %d", stats.LastGC.UnixNano(), mstats.LastGC)
    41  	}
    42  	n := int(mstats.NumGC)
    43  	if n > len(mstats.PauseNs) {
    44  		n = len(mstats.PauseNs)
    45  	}
    46  	if len(stats.Pause) != n {
    47  		t.Errorf("len(stats.Pause) = %d, want %d", len(stats.Pause), n)
    48  	} else {
    49  		off := (int(mstats.NumGC) + len(mstats.PauseNs) - 1) % len(mstats.PauseNs)
    50  		for i := 0; i < n; i++ {
    51  			dt := stats.Pause[i]
    52  			if dt != time.Duration(mstats.PauseNs[off]) {
    53  				t.Errorf("stats.Pause[%d] = %d, want %d", i, dt, mstats.PauseNs[off])
    54  			}
    55  			if max < dt {
    56  				max = dt
    57  			}
    58  			if min > dt || i == 0 {
    59  				min = dt
    60  			}
    61  			off = (off + len(mstats.PauseNs) - 1) % len(mstats.PauseNs)
    62  		}
    63  	}
    64  
    65  	q := stats.PauseQuantiles
    66  	nq := len(q)
    67  	if q[0] != min || q[nq-1] != max {
    68  		t.Errorf("stats.PauseQuantiles = [%d, ..., %d], want [%d, ..., %d]", q[0], q[nq-1], min, max)
    69  	}
    70  
    71  	for i := 0; i < nq-1; i++ {
    72  		if q[i] > q[i+1] {
    73  			t.Errorf("stats.PauseQuantiles[%d]=%d > stats.PauseQuantiles[%d]=%d", i, q[i], i+1, q[i+1])
    74  		}
    75  	}
    76  
    77  	// compare memory stats with gc stats:
    78  	if len(stats.PauseEnd) != n {
    79  		t.Fatalf("len(stats.PauseEnd) = %d, want %d", len(stats.PauseEnd), n)
    80  	}
    81  	off := (int(mstats.NumGC) + len(mstats.PauseEnd) - 1) % len(mstats.PauseEnd)
    82  	for i := 0; i < n; i++ {
    83  		dt := stats.PauseEnd[i]
    84  		if dt.UnixNano() != int64(mstats.PauseEnd[off]) {
    85  			t.Errorf("stats.PauseEnd[%d] = %d, want %d", i, dt.UnixNano(), mstats.PauseEnd[off])
    86  		}
    87  		off = (off + len(mstats.PauseEnd) - 1) % len(mstats.PauseEnd)
    88  	}
    89  }
    90  
    91  var big []byte
    92  
    93  func TestFreeOSMemory(t *testing.T) {
    94  	// Tests FreeOSMemory by making big susceptible to collection
    95  	// and checking that at least that much memory is returned to
    96  	// the OS after.
    97  
    98  	const bigBytes = 32 << 20
    99  	big = make([]byte, bigBytes)
   100  
   101  	// Make sure any in-progress GCs are complete.
   102  	runtime.GC()
   103  
   104  	var before runtime.MemStats
   105  	runtime.ReadMemStats(&before)
   106  
   107  	// Clear the last reference to the big allocation, making it
   108  	// susceptible to collection.
   109  	big = nil
   110  
   111  	// FreeOSMemory runs a GC cycle before releasing memory,
   112  	// so it's fine to skip a GC here.
   113  	//
   114  	// It's possible the background scavenger runs concurrently
   115  	// with this function and does most of the work for it.
   116  	// If that happens, it's OK. What we want is a test that fails
   117  	// often if FreeOSMemory does not work correctly, and a test
   118  	// that passes every time if it does.
   119  	FreeOSMemory()
   120  
   121  	var after runtime.MemStats
   122  	runtime.ReadMemStats(&after)
   123  
   124  	// Check to make sure that the big allocation (now freed)
   125  	// had its memory shift into HeapReleased as a result of that
   126  	// FreeOSMemory.
   127  	if after.HeapReleased <= before.HeapReleased {
   128  		t.Fatalf("no memory released: %d -> %d", before.HeapReleased, after.HeapReleased)
   129  	}
   130  
   131  	// Check to make sure bigBytes was released, plus some slack. Pages may get
   132  	// allocated in between the two measurements above for a variety for reasons,
   133  	// most commonly for GC work bufs. Since this can get fairly high, depending
   134  	// on scheduling and what GOMAXPROCS is, give a lot of slack up-front.
   135  	//
   136  	// Add a little more slack too if the page size is bigger than the runtime page size.
   137  	// "big" could end up unaligned on its ends, forcing the scavenger to skip at worst
   138  	// 2x pages.
   139  	slack := uint64(bigBytes / 2)
   140  	pageSize := uint64(os.Getpagesize())
   141  	if pageSize > 8<<10 {
   142  		slack += pageSize * 2
   143  	}
   144  	if slack > bigBytes {
   145  		// We basically already checked this.
   146  		return
   147  	}
   148  	if after.HeapReleased-before.HeapReleased < bigBytes-slack {
   149  		t.Fatalf("less than %d released: %d -> %d", bigBytes-slack, before.HeapReleased, after.HeapReleased)
   150  	}
   151  }
   152  
   153  var (
   154  	setGCPercentBallast any
   155  	setGCPercentSink    any
   156  )
   157  
   158  func TestSetGCPercent(t *testing.T) {
   159  	testenv.SkipFlaky(t, 20076)
   160  
   161  	// Test that the variable is being set and returned correctly.
   162  	old := SetGCPercent(123)
   163  	new := SetGCPercent(old)
   164  	if new != 123 {
   165  		t.Errorf("SetGCPercent(123); SetGCPercent(x) = %d, want 123", new)
   166  	}
   167  
   168  	// Test that the percentage is implemented correctly.
   169  	defer func() {
   170  		SetGCPercent(old)
   171  		setGCPercentBallast, setGCPercentSink = nil, nil
   172  	}()
   173  	SetGCPercent(100)
   174  	runtime.GC()
   175  	// Create 100 MB of live heap as a baseline.
   176  	const baseline = 100 << 20
   177  	var ms runtime.MemStats
   178  	runtime.ReadMemStats(&ms)
   179  	setGCPercentBallast = make([]byte, baseline-ms.Alloc)
   180  	runtime.GC()
   181  	runtime.ReadMemStats(&ms)
   182  	if abs64(baseline-int64(ms.Alloc)) > 10<<20 {
   183  		t.Fatalf("failed to set up baseline live heap; got %d MB, want %d MB", ms.Alloc>>20, baseline>>20)
   184  	}
   185  	// NextGC should be ~200 MB.
   186  	const thresh = 20 << 20 // TODO: Figure out why this is so noisy on some builders
   187  	if want := int64(2 * baseline); abs64(want-int64(ms.NextGC)) > thresh {
   188  		t.Errorf("NextGC = %d MB, want %d±%d MB", ms.NextGC>>20, want>>20, thresh>>20)
   189  	}
   190  	// Create some garbage, but not enough to trigger another GC.
   191  	for i := 0; i < int(1.2*baseline); i += 1 << 10 {
   192  		setGCPercentSink = make([]byte, 1<<10)
   193  	}
   194  	setGCPercentSink = nil
   195  	// Adjust GOGC to 50. NextGC should be ~150 MB.
   196  	SetGCPercent(50)
   197  	runtime.ReadMemStats(&ms)
   198  	if want := int64(1.5 * baseline); abs64(want-int64(ms.NextGC)) > thresh {
   199  		t.Errorf("NextGC = %d MB, want %d±%d MB", ms.NextGC>>20, want>>20, thresh>>20)
   200  	}
   201  
   202  	// Trigger a GC and get back to 100 MB live with GOGC=100.
   203  	SetGCPercent(100)
   204  	runtime.GC()
   205  	// Raise live to 120 MB.
   206  	setGCPercentSink = make([]byte, int(0.2*baseline))
   207  	// Lower GOGC to 10. This must force a GC.
   208  	runtime.ReadMemStats(&ms)
   209  	ngc1 := ms.NumGC
   210  	SetGCPercent(10)
   211  	// It may require an allocation to actually force the GC.
   212  	setGCPercentSink = make([]byte, 1<<20)
   213  	runtime.ReadMemStats(&ms)
   214  	ngc2 := ms.NumGC
   215  	if ngc1 == ngc2 {
   216  		t.Errorf("expected GC to run but it did not")
   217  	}
   218  }
   219  
   220  func abs64(a int64) int64 {
   221  	if a < 0 {
   222  		return -a
   223  	}
   224  	return a
   225  }
   226  
   227  func TestSetMaxThreadsOvf(t *testing.T) {
   228  	// Verify that a big threads count will not overflow the int32
   229  	// maxmcount variable, causing a panic (see Issue 16076).
   230  	//
   231  	// This can only happen when ints are 64 bits, since on platforms
   232  	// with 32 bit ints SetMaxThreads (which takes an int parameter)
   233  	// cannot be given anything that will overflow an int32.
   234  	//
   235  	// Call SetMaxThreads with 1<<31, but only on 64 bit systems.
   236  	nt := SetMaxThreads(1 << (30 + ^uint(0)>>63))
   237  	SetMaxThreads(nt) // restore previous value
   238  }
   239
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